1. Field of the Invention
This invention relates to treatment of nonmetallic refractory materials so as to facilitate bonding of the materials to one other or to metallic components.
2. Discussion of the Known Art
Refractory materials such as ceramics are often used in applications that require joining of such materials to either other ceramics or to metal components. For example, in the automotive industry, ceramics are used for many parts including wear pads that are joined to metal parts to prolong the service life of the parts. In another example, technical ceramics are used in many electrical and electronic applications such as power grid tubes, vacuum interrupters, semi-conductor packaging, multilayer substrates, ball grid arrays, power dissipation packages, and sensor packages.
Refractory materials such as ceramics have in the past been difficult to join together or to metallic components. Conventionally, metallization processes had to be performed on a ceramic prior to joining it to another ceramic or to a metal body because existing brazing formulations do not adequately wet a refractory surface. Typically, these processes involve multiple steps that form a bridge between the surface of the refractory material and braze filler metals, solder metals, or conductive/protective metals used to construct circuits on the material.
One example of a conventional metallization process relating to ceramic as the refractory body involves four major steps:                1. applying the desired area of the refractory material which is to be metal lized (usually screened on) with a molybdenum or molybdenum/manganese paste, and then air drying or drying in an infrared oven (e.g. at about 90 deg. C. to about 100 deg C. for about 10 to about 15 minutes);        2. firing the product of step 1 above in a controlled atmosphere (e.g. wet hydrogen) kiln at about 1200° C. to about 1500° C.;        3. cleaning, etching and nickel plating either with an electroless or an electrolytic process the product of step 2 above, and re-firing to sinter nickel into the molybdenum/manganese coating; and        4. adding brazing filler metal in the form of a wire, foil, ring, preform or powdered metal in between the metallized sections of the refractory body or bodies and then heating or firing to a temperature above the liquidus of the brazing filler metal in an oxygen free environment such as argon, dry hydrogen, ammonia gas, or vacuum.        
For electronic currents application, there can be additional steps of cleaning and activating the nickel layer and over plating with gold, silver, copper, or tin.
Another composition and method used with refractory materials is disclosed in U.S. Pat. No. 5,340,012, which is incorporated by reference herein. See also U.S. Pat. Nos. 3,063,144 (Nov. 13, 1962), and No 5,056,702 (Oct. 15, 1991).